Heat exchangers commonly include arrays of substantially rigid tubular conduits interconnected to one another, whether in series or parallel or other configuration, and located collectively between a plurality of liquid or gaseous fluids located respectively inside and outside them at diverse temperatures and pressures. Most often the tubular walls serving as a barrier between one contained fluid and another or between a contained fluid and the surrounding atmosphere are made of metals because of their desired rigidity and heat-conductivity, but some are composed of inelastic graphite. Tubing walls are designedly thin enough for ready heat conduction through them but thick enough to resist deformation conducive to leakage. Heat exchanger tubes must resist long periods of sustained pressure and temperature and numerous cycles between diverse pressures and temperatures without leaking. Other substantially rigid tubular conduits, not primarily heat exchangers., such as are used especially in chemical processing plants, contain a variety of fluids capable of considerable physical damage and personal injury if allowed to leak.
In the event of leakage, prompt efforts are often made to plug all leaking tubes, so as to continue operations, facilitate maintenance, protect the environment, save the contents (and money), etc. Plugging is complicated under any circumstances and is especially difficult where, as is common, the tubular interior is under much higher pressure than the exterior. Plugs satisfactory at low inside pressures may leak or even be blown out at higher pressures.
Existing methods of attacking this problem focus upon inserting the smaller end of a tapered stopper manually into the bore of such tubular conduit and applying force to its larger end, usually intermittently as by hammering it, until a substantial part or all of the stopper has entered the bore. Unfortunately, such procedure can not lodge a stopper sufficiently tightly to preclude subsequent leakage or outright expulsion of the stopper at high fluid pressure inside.
Surfaces of tubing walls and entrances in heat exchangers and chemical processing equipment are often made irregular by corrosion, erosion, scaling, and like occurrences. Forcing stoppers thereinto or therealong abrades them and is deleterious to effective plugging.
Examples of plugging means and methods using such objectionable forcing of stoppers into or along such tubing entrances or walls are found in Sharp U.S. Pat. No. 278,612 and in Japanese patent application 54-153807 of 29 Nov. 1979 published as 56-77698 on Jun. 26, 1981.
Similar insertion of circumferentially grooved cushion pads into apertures in sheet material, for retention with their opposite ends protruding at both sides of the sheet, is disclosed in Smith U.S. Pat. No. 2,457,930, where no leakage issue was presented or solved.
Tubing with walls insufficiently rigid (appreciably flexible) that they will expand at some internally applied fluid pressures cannot be effectively plugged by introducing stoppers thereinto so long as the wall can expand appreciably beyond the plug at higher applied internal pressures. Flexible tubings can have cleaning plugs forced therethrough by air or similar propellant fluid, with or without added lubricant, as in Weis U.S. Pat. No. 1,715,442, or can receive moderately soft or hard inserts therein, as in Bruner U.S. Pat. No. 2,830,361 (rigid sleeve of glass or the like inside rubber or like flexible tube) and Goldstein U.S. Pat. No. 3,139,677 (weatherstripping inside flexible sheath). Because of their inherent expansibility flexible tubes cannot be rendered leakproof by such means or method.
My present invention is directed to plugging whatever tubular conduits are sufficiently rigid to retain plugging stoppers over the range of temperatures and pressures designed for or subjected to.